In light-sensitive silver halide X-ray photographic materials for medical use, images are required to have a good sharpness and an excellent graininess so that niduses can be early detected and also misdiagnosis can be prevented in the photographing of any parts of living bodies.
The sharpness and graininess of light-sensitive materials influence the clearness of an image and the amount of its information, and hence are very important for improving the diagnostic performance.
In general, the parts of living bodies on which X-ray photographs are most often taken are the stomach, the chest and the bones in hand and foot. In order to improve the diagnostic performance in the photographing of them, it is necessary to give an image having a broad latitude of exposure over a low-density region to a high-density region, also having an appropriate density, free from fill-in or blank areas, and having a good sharpness.
As a parameter that determines the latitude of exposure of light-sensitive materials, gamma (.gamma.) is used. In presently commercially available light-sensitive materials for X-ray photography can be roughly grouped in three types, the high-.gamma. film, the low-.gamma. film and the medium-.gamma. film, which are used properly according to purpose. In these films, the high-.gamma. type has an excellent sharpness but on the other hand has the disadvantage that a low-exposure area may be filled in to decrease the amount of information. The low-.gamma. type can enjoy a satisfactory amount of information because of its broad latitude of exposure but may lack in sharpness. The medium-.gamma. type is on a middle level in both the sharpness and the latitude of exposure. Thus, under existing circumstances, they have merits and demerits.
A great number of techniques have been hitherto proposed to make progress or improvement in photographic performance, e.g., contrast and good graininess and sharpness in respect of silver halide emulsions. For example, the present applicant has disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as "Japanese Patent O.P.I. Publication") No. 214027/1984, a light-sensitive silver halide X-ray photographic material in which gamma obtained using a specific developing solution is defined, or in Japanese Patent O.P.I. Publication No. 116346/1986 the one in which gammas (.gamma.1 to .gamma.3) in specific regions are defined.
Including these techniques, however, most of conventional techniques have a difficulty in satisfying both the sharpness and the latitude, and, under actual circumstances, have not succeeded in achieving a high diagnostic performance in all instances where any of the aforesaid parts of living bodies are photographed.
Meanwhile, in parallel with the gamma (.gamma.), light-sensitive materials for X-ray photography are required to have a high sensitivity since a radiation exposure must be decreased.
Films with high sensitivity, all of which make use of silver halide grains with a large grain size, are disadvantageous in that they commonly have a poor resistance to mechanical pressure, compared with films making use of small-size grains.
For example, in the case of X-ray films, they frequently undergo mechanical pressure when mechanically transported in automatic exposure or automatic developing, or are folded or bent when sheetlike films are manually directly handled.
The pressure applied to films on such various occasions is known to cause changes in the photographic performance of silver halide grains, as reported in detail in, for example, K. B. Mather, J. Opt. Soc. Am. 38, 1054 (1948), P. Faelens and P. de Smet, Sci. et Ind. Phot. 25, No. 5, 175 (1954) and P. Faelens, J. Phot. Sci., 2, 105 (1954).
In the case of X-ray films, there is a possibility that a serious difficulty occurs in diagnosis when the part subjected to the pressure has been blackened. Hence, it is earnestly sought to provide a light-sensitive material whose photographic performance can not be adversely affected at all by the pressure applied.
As methods of improving pressure resistance, a number of techniques have been already proposed. Most of them rely on approaches from physical properties, making utilization of an adsorptivity reducing compound with which silver halide surfaces are covered, or a binder component. Hence, most of them have damaged any photographic performance, and the advent of a new technique has been strongly sought thereon together with the improvement in the sharpness and the latitude.